INTERDISCIPLINARY RESEARCH METHODS CORE Abstract The Interdisciplinary Research Methods (IRM) Core provides cutting-edge analytical and research design support to HIV researchers at CIRA and within the New England HIV Implementation Science Network. HIV research requires complex and innovative research designs and methods. The increasing focus on Implementation Science (IS), the integration of behavioral and biomedical approaches, and the study of HIV comorbidities such as substance use and mental health, presents challenges to the design and implementation of HIV research. Developing and applying statistical methods to address these complexities and to support CIRA's emphasis on IS is the focus of the IRM Core. Given CIRA's emphasis on research in small urban areas, methods of relevance to these settings will be incorporated in the IRM repertoire. Such areas pose statistical problems that challenge standard approaches to data analysis such as smaller sample sizes, high rates of missing data, geographic clustering of data and smaller social network sizes. The Core has developed methods to address these statistical problems such as the development of a strong geographical information systems (GIS) capacity, application of Bayesian techniques for missing data estimation, strong capacity in respondent driven sampling (RDS) for recruitment of highly stigmatized and hard to reach populations, expertise in innovative IS designs (e.g., SMART designs, stepped wedge), mixed method techniques, mathematical modeling and cost benefit analyses, and machine learning techniques to model causality. The IRM Core will provide consultation on, and training on IS and other research methods. The Core will provide in-depth and practical training on central concepts associated with HIV implementation research, with sessions on methods that have relevance to community-based research and IS, such as research on social networks, geospatial information studies, dissemination, stepped care, and adaptive treatment designs. The Core will also play an active role in assessing and analyzing the work of the New England HIV Implementation Science Network that was established by CIRA and others in 2014. The Core comprises three areas of expertise that are essential to IS, including: Quantitative Methods and Biostatistics; Qualitative Methods and Ethnography; and Operations Research and Mathematical Modeling. Dr. Trace Kershaw, Core Director, Professor and Chair of Social Behavioral Sciences Department at Yale School of Public Health, brings over 20 years of experience conducting HIV behavioral and intervention studies. Dr. Russell Barbour, Associate Director, is a statistician trained in ecological studies with expertise in multivariate and longitudinal statistics, spatial statistics, graph theory based network analysis, and advanced sampling techniques. He will provide data analysis, consultation services, and software training, and oversee Core evaluation and monitoring. Other contributing Core scientists will participate in Core seminars, consultations, and meetings.